The present invention relates to an apparatus and a method for controlling a target distance between two traveling vehicles and actuating a warning device and a recording medium for storing related program.
To reduce the driver's burden, an apparatus for automatically controlling a distance between two traveling vehicles is conventionally proposed. According to a conventional automatic distance control, the vehicle is accelerated or decelerated based on a difference between an actual distance and a predetermined target distance, a relative speed, and a relative acceleration between two traveling vehicles. For example, Unexamined Japanese patent publication 5-105047 discloses a control system which calculates a target throttle opening degree based on a difference between an actual inter-vehicle distance and a target distance as well as a relative speed between two traveling vehicles, and calculates a target hydraulic braking pressure based on an acceleration of a preceding vehicle. The vehicle is accelerated or decelerated based on the target throttle opening degree and the target hydraulic braking pressure thus obtained, so as to eliminate unpleasant anti-accelerative feeling given to passengers aboard on vehicle at the time the braking is unintendedly applied due to a tiny change of relative speed. The target hydraulic braking pressure, once calculated, is not reduced during the braking operation.
However, according to the above-described conventional control system, the control system may erroneously detect the relative speed or relative acceleration as a negative value due to measuring error of a distance sensor. In such a case, to prevent two vehicles from approaching too closely, the control system activates the braking device to decelerate the following vehicle to maintain an adequate distance between two vehicles. This will give unpleasant feeling to passengers aboard on the vehicle since there is no circumstances requiring the braking operation.
In general, the relative acceleration is obtained by differentiating a relative speed, for example, according to the following formula.{Relative speed (present value)−Relative speed (previous value)}/Distance measuring period
However, the relative acceleration calculated by using this formula tends to include noise if the measuring accuracy of the distance sensor is insufficient. The relative acceleration signal including such a noise component will induce erroneous activation of the braking device and cause the above-described problem.
Some of distance sensors, such as laser radar, cannot directly detect a relative speed. Therefore, the relative speed is calculated based on change of distance. The relative acceleration is obtained as a second-derivative value of the distance. Thus, measuring error of the distance sensor gives very large influence to the accuracy of calculated relative acceleration.
In this manner, accuracy of the relative acceleration has very important role in the inter-vehicle control performed based on the relative acceleration.
Similar problem occurs in a warning control for generating warning (e.g., sound, indication or the like) when two traveling vehicles are too closely positioned. For example, the unexamined Japanese patent publication 8-132996 discloses a warning system which performs warning calculation based on the relative speed and the relative acceleration. If the relative acceleration is a signal including a significant noise component, the warning operation will result in error.